At least £469 million. In 2011 the British National Audit Office (NAO) attributed that amount to skipping stakeholders in FiReControl, a large government programme for fire control centres.
One case, not a statistic
The NAO assessment covers a single project. That does not make the amount any less serious, but it makes it a case rather than a law. You cannot derive a percentage or a probability from it, and you should not try. What it does show: a stakeholder you skipped can later become a cost item far larger than the conversation you did not have.
The pattern you will recognise
Suppose a municipality replaces the system that handles permit applications. This is an illustrative example, not a described project. The project document looks well put together. It contains the supplier's risks, the planning, the licences and the migration. The stakeholder list names the steering group, the project manager and the supplier. The permits department, which works with the system every day, appears as 'keep informed'. The supervisor is not on the list.
Nobody did anything wrong. The list was drawn up from whoever already sits at the table. Such a list rarely comes from unwillingness. It comes from habit: you start with the people you know. That is exactly the mechanism to recognise: a list that contains only the parties you already know, because they are the ones already at the table.
Two questions for your own risk analysis
Take your risk analysis and ask two questions about each of the largest risks. Who has a stake in this, and has that party already been heard? And: who would notice this risk first but is not in the meeting?
The second question is the harder one. The people who use the system every day often notice deviations before the steering group does. If that voice is missing, you miss the signal, even when your risk list looks tidy.
What RisicoRadar does and does not do here
RisicoRadar scans project documents on five risk sectors. One of them is Stakeholders & Communication. So the document is checked on that sector. The product does not know your stakeholders, and it assesses the document, not your project. A thin paragraph on stakeholders says something about the text. It cannot say whether the project is low-risk or high-risk. The same holds in reverse: a document without such a paragraph is not the same as a project without stakeholders.
Moreover, no validated scoring instrument stands behind the outcome. Use a signal as a reason to read your own text critically, not as a verdict.
Where to start next week
Pick up your next project document and find the stakeholder paragraph. Choose the three largest risks and ask about each: which party has a stake in this, and has that party already responded? If the answer for one risk is 'nobody', you know where to go first.